Known in the prior art is a method in which a valve having a housing with a shut-off member is placed into the seat of a tightness checking apparatus, said seat having a resilient member disposed around its periphery, and the valve housing is pressed against the resilient member, then a vacuum is created in the seat cavity under the valve which is exposed to the vacuum during a time interval required for checking the valve, whereupon a force is applied to the valve in a direction opposite to the force of pressing, said force being slightly higher than the valve weight, and faulty valves are removed under the action of said force from the seats while sound valves are conveyed further to a station where they are removed from the seats.
Also known in the art is an apparatus for effecting said method, comprising a bed with a driving shaft vertically disposed thereon, and a rotor mounted on the shaft. Seats for the valves to be placed therein are rigidly secured on the rotor, being evenly spaced around the rotor circumference. The valves are checked together with spray heads fitted therein. The upper portion of each seat is provided with a resilient member shaped as a ring which ensures a tight contact between the seat and the valve housing. Mounted under each seat is a means for creating vacuum in the seat cavity under the valve. This means is essentially a cylinder with a piston, communicating through a channel with the seat cavity. The total space of the seat cavity under the valve, the communicating channel and the cylinder space between the piston in the initial position and the cylinder end is the initial volume of the cavity under the valve to be checked.
A train of levers links the piston with a cam mounted on the bed. When the rotor with the seats is rotated, the configuration of the cam determines the amount of the piston displacement.
Mounted over each seat in the rotor is a means for placing the valve into the seat, pressing the valve against the seat resilient member, opening the valve, and removing the valve from the seat. The means for pressing the valve against the seat and removing it from the seat includes a lever whose pin is secured to the rotor, while the means for opening the valve prior to its removal from the seat is mounted on the lever itself.
The vacant end of the lever carries a spring-biased magnet mounted thereon for picking up valves to be checked from a trough which is located somewhat higher than the seat, in a direction radial with respect to the rotor. In addition, mounted on the lever end is a stem for opening the valve by pressing the head thereof.
Each seat is provided with a pipeline to supply compressed air to the valves with faulty spray heads which remain in the rotor seats after the sound valves have been removed.
Each seat with the means associated therewith for effecting the operations described above make-up an operating position of the rotor.
All means of the operating positions are set in action each by their own cam.
The cam configuration actuating the lever for pressing the valves against the seat resilient member is profiled so as to ensure lowering of the lever after the magnet has picked up the next valve in turn from the supply trough, holding the lever in the lower position when vacuum is created in the cavity under the valve and exposure of the valve to the vacuum, lifting the lever to remove a faulty valve from the seat, lowering and holding the lever in the lower position during the stem operation which opens the valve, lifting the lever with the magnet to remove a tight valve with a sound head from the seat, holding the lever in the upper position to transfer the removed valve into the receiving trough and to eject the valve with a faulty head by compressed air from the seat into a corresponding trough, as well as for picking up another valve to be checked by the magnet from the supply trough.
The cam configuration actuating the piston to create vacuum in the cavity under the valve is profiled so as to ensure displacement of the piston in the cylinder immediately after the valve has been pressed against the seat resilient member and to return the piston to the initial position upon extracting the tight valve with sound head from the seat.
The cam configuration actuating the stem to open the shut-off member of the valve is profiled so as to ensure the stem stroke required for opening the valve and holding it in this position for a period of time sufficient for air to pass into the cavity under the valve prior to removing the tight valve from the seat.
The prior art apparatus for checking valves for tightness described above operates as follows.
The driving shaft mounted on the bed continuously rotates the rotor together with the operating positions. The magnet mounted on the lever end picks-up a valve to be checked from the supply trough and places it on the rotor seat. Then the same magnet which is a part of the means for pressing the valve presses the valve housing against the seat resilient member. Simultaneously, the piston of the means for creating vacuum in the seat cavity under the valve is displaced in the cylinder, acted upon by its own cam. Therefore, a vacuum is created in the seat cavity under the valve. The valve is further moved together with the rotor during a time period required for changing the degree of vacuum in the cavity under the valve if the latter is faulty. The amount of this time is directly proportional to the volume of the cavity under the valve. In the prior art apparatus, this volume includes the space of the seat cavity under the valve, the space of the communicating channel, and the space of the cylinder of the means for creating the vacuum, the space of the seat cavity itself being several times smaller than the total space of the channel and the cylinder space. During the entire period of exposing the valve to the vacuum, the spring-biased magnet on the lever end according to the configuration of the cam controlling said magnet is held in the extreme lower position, pressing the valve against the seat resilient member. At the same time, all other means of the operating position of each seat are moved together with the rotor taking no part in operation.
After the exposure time is over the lever is pivoted around its pin. The lever end with the magnet mounted thereon is lifted upward to extract the valve being checked from the seat.
If the valve is tight, it is held in the seat by the atmospheric pressure and the force of the magnet is not sufficient to extract it from the seat. If the valve is faulty, there is practically no vacuum in the seat cavity under the valve, thus enabling the magnet to extract such a valve and transfer it to the trough for rejected valves which is mounted slightly higher than the seat in a direction radial with respect to the rotor. The tight valves remain in the seats and are moved further together with the rotor. During this movement the lever acted upon by the cam is lowered and the spring-biased magnet comes into contact with the valve housing while the stem of the means for opening the valve depresses the valve spray head thereby opening the valve.
When the head is in proper condition, the air passes into the cavity under the valve, eliminating the vacuum therein. A faulty head does not let the air pass and the valve remains held in the seat by the atmospheric pressure.
After the pressure in the cavity under the valve becomes equal to the atmospheric pressure, the lever is pivoted around its pin. The lever end with the magnet is lifted upward. The valves with sound heads are extracted by the magnets from the seats and transferred into the trough for sound valves.
The valves with faulty heads which failed to admit air into the cavity under the valve are not extracted by the magnets and are moved further towards the compressed air pipeline where the valve is blown off into the trough for valves with faulty heads.
Then the cycle is repeated.
The known method of checking the valves for tightness has a number of disadvantages the main one of which is that the vacuum in the cavity under the valve is created by increasing its volume. This, in turn, requires a significant time of exposing the valve to vacuum since this time is directly dependent on the volume of the cavity under the valve.
In order to accomplish this method of creating a vacuum in the cavity under the valve, the prior art apparatus includes a means comprising a cylinder with a piston, communicated by a channel with the cavity of the seat intended for fitting therein the valve to be checked. The total volume of the cylinder and the communicating channel is several times larger than the volume of the cavity of the seat itself, whereby a significant time of exposing the valve to the vacuum is required because this time is directly proportional to the total volume of the space under the valve. This is one of the disadvantages of the known apparatus.
Another drawback of the known apparatus is that during the time of exposing the valve to vacuum all the means which are provided for each position of the rotor are standing idle. This drawback considerably limits the productivity of the known apparatus since it may be increased only by mounting additional operating positions onto the rotor which will require a large diameter of the rotor.
Still another disadvantage of the prior art structure consists in that a magnet is used for extracting faulty valves, thereby limiting the range of materials from which the valve housing could be manufactured.